A very interesting horn driver project presented by Microchip technology is presented in this circuit diagram . This horn driver project is based on PIC16F886 microcontroller , from Microchip . This microcontroller horn driver circuit diagram is very simple and require few external components . The PIC MCU has peripheral resources within the device to provide horn driver services in a very simple manner.

The PIC MCU peripherals include the Enhanced CCP (ECCP) module in Pulse-Width Modulation (PWM) Half-Bridge mode to drive the 2 horn drive leads and a single ADC input to monitor the horn feedback after it has been conditioned.

Horn characteristics are required to determine the defined parameters for the range of the PWM module.

For example , a horn with a resonant frequency of 3.5 kHz ± 0.5 kHz; the PWM module generates a PWM frequency output from 3 kHz to 4 kHz with 50% duty cycle.

With a device that is running off of the internal oscillator at 8 MHz, the clock source to Timer2 that drives the PWM period generates 2M clocks per second. For a 3 kHz period, this is 667 clocks per cycle, and for a 4 kHz period, this is 500 clocks per cycle. Because Timer2 is an 8-bit timer, accepting only a maximum value of 255, these clocks per cycle must be divided (a prescaler of divide-by-4, yielding 166 clocks per cycle for 3 kHz, and 125 clocks per cycle for 4 kHz) .

The PWM output driven by the ECCP module in Half-Bridge mode, with both the P1A and P1B outputs active-high, will step through the 125 through 166 clocks per cycle periods at a period rate, and as the Period register is loaded, the value will be dividedby- 2 and loaded into the Duty Cycle register for a 50% duty cycle. This will become the new PWM period for measuring the feedback from the horn driver, and drives the transistor that raises the level that the horn lead sees, to 9V.

Software for this project was developed by Bill Anderson , Microchip Technology Inc..

Using microcontrollers you can design many interesting and useful electronic projects . This electronic project circuit is based on PIC16C622 microcontroller ( manufactured by Microchip ) . This PIC project is a simple resistance and capacitance “Pic Meter” which can measure resistance in the range 1W to 999W and capacitance from 1 nF to 999 nF.

This PIC METER uses a variation of the single-slope integrating converter.

All measured data are transmitted to a PC which displays the value measured.

This Pic Meter project is powered directly from the RS-232 serial port ,the RTS and DTR lines from the serial port output 3V to 11V to the PIC METER. The diodes D2 and D3 prevent any damage to the PC’s serial port.

Resistor R10 is used to current limit the Zener diode, D4. D4 is used to regulate the RTS and DTR voltage to 5.6V. Capacitors C3 and C4 provide power supply filtering to the Zener diode and the PIC16C622. Using this type of powering source for the PIC Meter will not damage the RS232 port , because this project has an very low current consumption of 7mA.

S1switch is used to select either a resistor or capacitor measurement. RB5 of the PIC16C622 is used to detect what type of component is being measured.

Resistor measurements that are started without any component connected to the measuring terminals will cause an error. Capacitor measurements without a component connected to the measuring terminals will give a result of 0 pF.

Switch S2 is used to initiate a measurement. The switch is connected to RB6 of the PIC16C622 and the

PORTB wake-up on change interrupt is used to detect a key press.

The charge time of the unknown RC network is measured using Timer0 , measured value is multiplied by the known value of resistance or capacitance and stored in an accumulator. Then the charge time of the known RC network is measured. The accumulator is divided by the known RC network charge time to give the value of resistance or capacitance of the unknown component.

This software and project was designed by Rodger Richey from Microchip Technology Inc.

You can measure temperature using various methods like : analog circuits , digital circuits or some other methods . This electronic project is a very simple thermometer that is based on the PIC16F84A microcontroller , designed by Microchip .

Why to use a thermometer that is designed using a microcontroller and not a classic analog thermometer ? because you can design a complex solution using few external components , resulting an low cost application that provide a high precision measurement .

This microcontroller project use watchdog timer function to measure temperature . The WDT on all PICmicro microcontrollers has a nominal time-out period of 18 ms. The WDT time-out period varies with temperature, VDD and part-to-part process variations. Without using a separate temperature sensor, it is possible to calculate the temperature with reasonable accuracy using the WDT time-out period.

To translate the environment temperature into an actual reading, the system must be able to do the following:

• Provide a method for establishing time-out to temperature calibration

• Count the number of WDT time-outs for a given period of time

• Equate the number of time-outs to a temperature

The system design also includes wake-on-interrupt key scanning and temperature display.

The circuit diagram is built around a PIC16F84A microcontroller, three seven segment

LEDs to display temperature. The common anode of each LCD is connected to PORTA<2:0> through PNP transistors, which are used to source the current for each digit. The entire device operates on a single 9V battery.

The PIC16F84A microcontroller is normally in SLEEP mode, consuming

very little operating current but if any key is pressed, it ‘wakes up’ from SLEEP and updates the WDT count, and checks for additional key presses. If there are none, it returns to SLEEP mode.

The WDT Thermometer has three distinct operating modes:

SLEEP Mode: This is the default mode the system starts in when power is applied .

Display Mode: When the TEMP key is pressed, the system wakes up and the LEDs show the temperature

in degrees Centigrade.

Calibration Mode: This mode creates a set of new calibration values, in addition to those present in the firmware.

To calibrate the device you must to :

1. Place the system in the temperature forcing system at the higher of the two calibration temperatures, and wait 5 minutes for the temperature to stabilize.

2. Press and hold the SET key while applying power to the system.

3. Press either the UP or DOWN key to increase or decrease the displayed temperature setting by one degree to match the actual temperature.

4. Press the SET key. The new high temperature calibration is stored in data EEPROM.

5. Change the temperature of the forcing system to the low calibration temperature (allow 5 minutes for the temperature to stabilize).

6. Press either the UP or DOWN key to increase or decrease the displayed temperature setting by one degree to match the current temperature.

7. Press the SET key. The new low temperature calibration is stored in data EEPROM, and the firmware sets a flag (Default) to indicate that new calibration information is available.

8. To return to the preprogrammed calibration at any time during this process, press the TEMP key.

This project ( hardware and software ) was designed by Leena Chaudhari from Microchip Technology Inc.

You can download source code for this PIC16F84A project by following this link